This invention relates to the use of high anti-leukemia activity responsive to the combination of hydroxamic acid analogue histone deacetylase inhibitors and PKC412 against human acute leukemia characterized as expressing phosphorylated (p)-FLT3 kinase by a novel flow cytometry based assay.
The majority of the patients with Acute Myeloid Leukemia (AML) are incurable with current forms of chemotherapy. In approximately 25% of AML the leukemia cells express a constitutively active form of auto-phosphorylated (p) FLT3 tyrosine kinase on the cell surface. The activity of p-FLT3 confers growth and survival advantage on the leukemic cells. Patients with acute leukemia, whose leukemia cells express p-FLT3 kinase activity, have a poor overall clinical outcome. PKC412 is a novel staurosporine analogue that inhibits p-FLT3 kinase activity and induces apoptosis (programmed cell death) of the leukemic cells. Although treatment with PKC412 results in the inhibition of p-FLT3 kinase activity, it fails to eradicate the leukemia cells and achieve durable clinical benefit. Therefore, it would be desirable to potently down-modulate the levels and activity of pFLT3 in leukemia cells to achieve maximum anti-leukemia effect. This effect would only be observed in those leukemia patients whose leukemia cells possess p-FLT3 kinase activity.
Therefore, to improve the overall benefit of the treatment strategies based on PKC412, it is important to identify those patients whose leukemia cells possess p-FLT3 kinase activity. So far the assays that have been employed to identify these patients have been cumbersome and slow, and difficult to implement in the clinical setting.
Accordingly, what is needed is a flow cytometry-based assay that would rapidly identify patients with acute leukemia, whose blasts possess surface expression of active p-FLT3.